1. Field of the Invention
The present invention generally relates to a user terminal, a server, and a controlling method thereof, and, more particularly, to a user terminal using an application content, which is partially encrypted, a server, and a controlling method thereof.
2. Description of the Related Art
A conventional Digital Rights Management (DRM) system is designed to manage the rights of digital content, which is reproduced by another player, such as a document, music and movie. Such a DRM system has been used to protect an application, which is executable digital content. Specifically, all digital content is encrypted and the encryption key is included in an object called a license, to which a provider's signature is added before being distributed. The distributed content and license are installed on a user's terminal, the license is parsed by a designated DRM client, and the content is decrypted using the encryption key and then executed by a designated viewer or player.
A conventional DRM system, which is designed to protect digital content such as music and movie, may decrypt the latter portion of the content while the former portion of the content is being reproduced, even though the entire content are encrypted. Therefore, encryption of content does not have a significant impact on its reproduction time. However, if an application is encrypted, the encrypted file must be decrypted in its entirety and only then can it be executed. Thus, the longer the decryption time is, the longer it takes to reproduce the application. Such delay in reproduction time may cause inconvenience to a user and reduce the user's desire to purchase.
While content such as music and movies are rarely updated once they are downloaded, an application must frequently be patched and updated. However, conventional DRM systems do not have a protocol to receive a license again when an application is updated. Therefore, it is difficult to use the conventional DRM system to protect an application.
The main purpose of a conventional DRM system is to protect content which must be reproduced and thus, the main purpose of DRM design is to guarantee the confidentiality of the content. On the other hand, in order to protect an application, combinability is more important than confidentiality.